Constant: The run of the partial waves inside the cells is assumed to be constant.
A highly dissipative first order scheme results.
This values will usually only be used for test (or comparison) purposes.

Minmod: Chooses the smallest slope which still results in a second order scheme.
It is the most diffusive (and most stable) one in this class.

VanLeer: (default) The recommended second order scheme.

Superbee: The ``most aggressive'' stable 2nd order scheme.
It results in the steepest shocks, which works well in some test cases
but might be to difficult for the radiation transport module to handle.

Usually, the VanLeer reconstruction is a good choice.
If a more stable (and diffusive) scheme is needed, take Minmod.
The PP reconstruction gives the highest accuracy.

real c_slopered:
When -Drhd_roe1d_slope_l01=2 is set (see Sect. 3.7),
a new extra stabilization mechanism can be activated:
If one of the reconstruction methods VanLeer, Superbee, or PP
(see Sect. 5.3.7) is activated, the slope can be reduced
(by averaging with the results from a MinMod reconstruction) by setting
c_slopered to a positive non-zero value.
This value can be set e.g. with

integer n_hydcellsperchunk:
In every directional sub-step neighboring 1D columns are independent from each other.
They can be grouped and computed in chunks of arbitrary size.
The approximate number of grid cells per chunk can be specified e.g. with

The exact number is determined at run time to get (approximately) equal sizes of the individual
chunks.
The choice of this parameter does not affect the result of the computation but
the memory usage and performance:
Smaller (and more) chunks may result in an optimum cache usage and need the smallest
amount of memory, but result in additional overhead due to frequent subroutine calls.
Bigger (and less) chunks are to be preferred for vector machines and processors
with large caches.
Very rough guide values may be

2500: Pentium III processor

20000: RISC processor

100000: Vector machine

Note: For simulations with activated OpenMP
on a parallel machine the chunk size has to be made small enough to
allow at least as many chunks as processors available. This is
particularly important for models with a small number of grid points
(e.g. 2D models).
An example is given for the Hitachi SR8000 in Sect. 3.8.5.

real c_visdrag:
This viscosity parameter controls the drag force which is (if requested)
applied inside the hydrodynamics routines themselves.
It does not act on velocity gradients as usual viscosity but applies a force proportional to the
velocity itself (but with the opposite sign).
The amount can be specified e.g. with

real c_visdrag f=E15.8 b=4 &
n='Drag viscosity parameter' u=1
0.001

The value gives the fraction the velocity is reduced per time step.
Therefore, reasonable values lie between 0.0 and 1.0.
In almost every case the drag forces will be switched off (c_visdrag=0.0).
If e.g. strong pulsation have to be damped in the initial phase of a simulation
a value around 0.001-0.01 seems appropriate.

real c_visbound:
An additional drag force can be added locally in inflow cells in the outer layer
when the transmitting boundary condition is chosen. The value can be
set e.g. with